Monday, September 15, 2014

New paper finds North Carolina sea levels rising < 7 inches per century

A new paper published in Quaternary Research reconstructs sea level rise in North Carolina over the past 1000 years and finds sea level rise since 1845 has been only 1.71 mm/year, equivalent to 6.7 inches per century and in line with many other papers finding global sea level rise of less than 7 inches per century.Data from the paper indicates no evidence of acceleration since the end of the Little Ice Age in ~1850. No acceleration of sea level rise means no evidence of a man-made contribution. The data also shows that sea levels "paused" their natural 20,000 year rise during the Little Ice Age from ~1,200 to ~164 years ago.

Salt-marsh sediments provide accurate and precise reconstructions of late Holocene relative sea-level changes. However, compaction of salt-marsh stratigraphies can cause post-depositional lowering (PDL) of the samples used to reconstruct sea level, creating an estimation of former sea level that is too low and a rate of rise that is too great. We estimated the contribution of compaction to late Holocene sea-level trends reconstructed at Tump Point, North Carolina, USA. We used a geotechnical model that was empirically calibrated by performing tests on surface sediments from modern depositional environments analogous to those encountered in the sediment core. The model generated depth-specific estimates of PDL, allowing samples to be returned to their depositional altitudes. After removing an estimate of land-level change, error-in-variables changepoint analysis of the decompacted and original sea-level reconstructions identified three trends. Compaction did not generate artificial sea-level trends and cannot be invoked as a causal mechanism for the features in the Tump Point record. The maximum relative contribution of compaction to reconstructed sea-level change was 12%. The decompacted sea-level record shows 1.71 mm yr− 1 of rise since AD 1845.